Relector-use precoat metal plate

ABSTRACT

The present invention provides a precoated metal sheet for light reflectors having a high diffuse reflectance of visible lights and an excellent heat absorptivity, and also provides the electric or electronic apparatus using it. The precoated metal sheet comprises a metal sheet or plated metal sheet, a visible light reflective coat on one surface of the sheet, and a heat absorptive coat on the other surface of the sheet. The visible light reflective coat has a diffuse reflectance of visible rays of not less than 0.7 in a wavelength of 400 to 700 nanometers. The heat absorptive coat has a total emissivity of infrared rays of not less than 0.7 in the range of wave number of 600 to 3000 cm −1  measured at a certain temperature within the range of from 80 to 200 degrees centigrade.

TECHNICAL FIELD

The present invention relates to a precoated metal sheet used as amaterial of a light reflector and to an electric or electronic apparatuswhich has a function to emit a visible ray and has a plate forreflecting the emitted visible ray, such as an illuminator, audiovisualequipment, mobile computing devices, a plasma display, and a liquidcrystal television set.

BACKGROUND ART

An illuminator, audiovisual equipment, an electronic apparatus, mobilecomputing devices, a liquid crystal television, a plasma display, andthe like have functions of making the surroundings bright, transmittinga light signal, projecting an optical image or the like, by emittingvisible rays. Some of these apparatus have a light reflector and improvethe luminance of light or change the direction of light by reflectinglight using the reflector. Therefore, in order to avoid the drop ofquantity of light when light reflects in a reflector, the surface of thereflector requires a high visible ray reflectance. As means forimproving the reflectance on the surface of a reflector in the past, forexample, a metal has been polished to make a mirror plane, or a whitecoating material with a high reflectance has been coated. Nippon SteelCorporation catalog “View coat” discloses a precoated steel sheet coatedwith a white coating material beforehand for light reflectors of anilluminator.

Japanese Unexamined Patent Publication No. Hei 10-000730 discloses alight reflecting film, excellent as a light reflector for a liquidcrystal display, comprising a substrate film, a thin metal film layerlaminated on one side of the substrate film, and a fine inorganicparticle-containing resin layer laminated on the thin metal film layer,wherein the thin metal film layer is made of aluminum, and thereflective indices n_(f) and n_(b) satisfy the relationshipn_(f)−n_(b)>=0.4 in which n_(f) is the refractive index of the fineinorganic particle and n_(b) is the refractive index of the resin.Japanese Unexamined Patent Publication No. 2002-172735 discloses ahighly diffusing reflective coated metal panel used as a reflectingplate for the back light of a liquid crystal display, comprising analuminum panel, an undercoat layer formed on the aluminum panel, and atopcoat layer formed on the undercoat layer, wherein the undercoat layercontains 100 parts by weight of a resin and 150 to 300 parts by weightof a titanium oxide pigment and has a film thickness of 50 to 100micrometers, and the topcoat layer contains 100 parts by weight of aresin and 100 to 250 parts by weight of a titanium oxide pigment and hasa gloss of not more than 15 and a film thickness of 10 to 30micrometers. However, the need to form a light reflector used for anilluminator and for an electric apparatus, such as a liquid crystaldisplay, into various shapes before use has been increasing with acomplication of the structure and design of an electric apparatus inrecent years.

However, when a film is used as a substrate as described in JapaneseUnexamined Patent Publication No. Hei 10-000730, it is difficult to forma film, laminated with a metal thin film layer or a resin layercontaining fine inorganic particles beforehand, into a target shape.Therefore, the film must be formed into the target shape in advancebefore laminating the metal thin film layer or the resin layercontaining fine inorganic particles. However, when a shape of a lightreflector is complicated, it is difficult to laminate a coat on theformed part with a uniform thickness.

On the other hand, according to the technique described in JapaneseUnexamined Patent Publication No. 2002-172735, after applying anundercoat layer and a topcoat layer to an aluminum plate beforehand, thecoated aluminum plate can be formed into a target shape. However, as theamount of titanium oxide added in a reflective coat was too high, thecoat was weak, and there were problems that cracks occurred in thereflective coat or the coat peeled at the time of forming. Moreover, italso has a weak point in that formed shapes are limited becausealuminum, which is the base metal does not have a good formingworkability. Furthermore, it is very difficult to coat an undercoat withsuch a thickness (50 to 100 micrometers) at one time by a roll coater ofa common precoating line, and it is necessary to coat two or more times,and therefore there is a weak point of low productivity.

Consequently, it was difficult to apply the light reflector described inJapanese Unexamined Patent Publications No. Hei 10-000730 or No.2002-172735 to an electric apparatus which must employ a light reflectorformed into a certain shape for the reasons of the structure or designof the electric apparatus, and it was necessary to employ a conventionalprecoated steel sheet for light reflectors of illuminators which wasbeforehand coated with a white paint.

On the other hand, the problem of generation of heat of an electricapparatus has occurred with the computerization of electric apparatus inrecent years. As means to solve this heat problem, Japanese UnexaminedPatent Publication No. 2002-228085 discloses a technique for improving aheat radiative property by making the emissivity of thermal radiation ofthe inner layer coating film of a metal surface not less than 70percent.

SUMMARY OF THE INVENTION

There is a growing demand for the above-mentioned electric apparatus tobe brighter and to have the same brightness in spite of using lesselectric power. There is also a growing demand for an electricapparatus, which must employ a light reflector formed into a certainshape, to be brighter and to have the same brightness in spite of usingless electric power.

The present invention aims at providing a precoated metal sheet forlight reflectors having an elevated diffuse reflectance of visible rays,a precoated metal sheet for light reflectors excellent in a heatabsorptivity, and an electric or electronic apparatus using the same.

The inventors have found that the brightness of illumination increasedwhen a heat absorptive coat was coated on one surface of a lightreflector having a coat excellent in a visible light reflectivity on theother surface thereof as a result of study.

The inventors also found the following:

When a titanium oxide is added to a fluororesin-containing binder resin,if the content of titanium oxide is too small, a visible ray passesthrough the coat, or the visible ray reflectivity of the coat is lowbecause the gross area of the interfaces between the binder resin andthe titanium oxide is small. As the content of titanium oxide increases,a visible ray transmittance through the coat decreases and the grossarea of the interfaces between the binder resin and the titanium oxideincreases and, therefore, the visible ray reflectivity of the coatimproves. It was found out, however, that if the content of titaniumoxide is more than a certain content, a volume of titanium oxide is muchlarger than a volume of the binder resin, and the interfaces between thebinder resin and the titanium oxide decreased conversely, and then thevisible ray reflectivity declines.

The present invention has been achieved based on this knowledge.

According to the invention, the followings are provided:

(1) A precoated metal sheet for light reflectors, comprising a metalsheet or plated metal sheet, a visible light reflective coat provided onone surface of the metal sheet or plated metal sheet, and a heatabsorptive coat provided on the other surface of the metal sheet orplated metal sheet, wherein the visible light reflective coat has adiffuse reflectance of visible rays of not less than 0.7 in a wavelengthof 400 to 700 nanometers, and the heat absorptive coat has a totalemissivity of infrared rays of not less than 0.7 in the range of wavenumber of 600 to 3000 cm⁻¹ measured at a certain temperature within therange of from 80 to 200 degrees centigrade.

(2) A precoated metal sheet for light reflectors according to (1) above,wherein the visible light reflective coat comprises a binder and atitanium oxide, a content of the titanium oxide being 40 to 250 parts byweight, based on 100 parts by weight of a solid content of the binder.

(3) A precoated metal sheet for light reflectors according to (1) or (2)above, wherein the binder in the visible light reflective coat comprisesa fluororesin.

(4) A precoated metal sheet for light reflectors according to any one of(1) to (3) above, wherein the heat absorptive coat comprises a binderand a heat absorptive pigment, a content of the heat absorptive pigmentbeing 10 to 150 parts by weight, based on 100 parts by weight of a solidcontent of the binder.

(5) A precoated metal sheet for light reflectors according to (4) above,wherein the heat absorptive pigment is a carbon.

(6) A precoated metal sheet for light reflectors according to (4) or (5)above, wherein the heat absorptive coat further comprises a conductivemetal powder, a content of the conductive metal powder being from 1 to50 parts by weight, based on 100 parts by weight of a solid content ofthe binder.

(7) A precoated metal sheet for light reflectors according to any one of(1) to (6) above, wherein the surface roughness Ra of the metal sheet orplated metal sheet is 0.05 to 1.8 micrometers.

(8) A precoated metal sheet for light reflectors according to any one of(1) to (7) above, wherein the metal sheet or plated metal sheet ispreferably a steel sheet or a plated steel sheet.

(9) An electric or electronic apparatus comprising a precoated metalsheet for light reflectors according to any one of (1) to (8) above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating one embodiment of aprecoated metal sheet according to the present invention.

FIG. 2 is a sketch of an instrument for measuring illumination.

DETAILED DESCRIPTION OF THE INVENTION

Light of a fluorescent lamp or an electric bulb used as an illuminatorand the light used for a light signal and the like are both visiblerays. Therefore, if a diffuse reflectance of visible rays on the surfaceof a light reflector is more improved, light will become bright as awhole. A diffuse reflectance of visible rays varies with a substance ofa light reflector surface. Aluminum, silver, titanium oxides, bariumsulfate, zinc oxides, and the like are known as a substance having ahigh diffuse reflectance of visible rays. Therefore, a light reflectorhaving a high reflectance is now made by using such technology, and itis thought that it is difficult to improve the reflectance.

On the other hand, an illuminator and a light signal-emitting instrumentemit heat, which is an infrared radiation, as well as emitting light.Moreover, these instruments are mostly equipped with electroniccomponents for controlling light brightness and other parts, and theseelectronic components generate heat.

The inventors found out that the light of an illumination or lightsignal becomes brighter when a precoated metal sheet coated with a highvisible light reflectance coat on one side and a heat absorptive coat onthe other side was used as a light reflector used for an illuminator ora light-signal-emitting instrument. Although the details of this reasonare unknown, it seems that because heat (infrared radiation) generatedfrom an illuminator or light signal-emitting instrument is probablyabsorbed by the heat absorptive coat, the luminous body acts in order tocompensate this, and the quantity of visible light also increases, andit becomes bright. Moreover, in addition to these phenomena, when heatis absorbed by a precoated metal sheet of the present invention via aheat absorptive coat, the temperature of the precoated metal sheetrises, the temperature of the visible light reflective coat also rises,the refractive index of a binder resin in the visible light reflectivecoat becomes low, the refractive index difference between an addedpigment, such as titanium oxides, and the binder resin becomes large, avisible ray reflectance of the visible light reflective coat improves,and the light of the illumination or light signal becomes brighter.

Furthermore, it is also considered to be one of causes of the brightnessimprovement that the heat emitted out of the instrument is absorbed bythe heat absorptive coat, the temperature in the instrument falls,electronic circuits of a control board and the like provided in theinstrument work efficiently, the electric current loss spent on thelight emission decreases, and the quantity of light increases. Oneembodiment of a precoated metal sheet for light reflectors excellent inheat absorptivity according to the present invention is illustrated inFIG. 1. It comprises a metal sheet 1, a visible light reflective coat 2provided on one surface of the metal sheet 1, and a heat absorptive coat3 provided on the other surface of the metal sheet 1.

A visible light reflective coat of the precoated metal sheet of thepresent invention must have a diffuse reflectance of visible rays of notless than 0.7 in the wavelength of 400 to 700 nanometers. A diffusereflectance of visible rays of less than 0.7 is unsuitable because itdoes not improve a visible light reflective function and reduces thelight from an illumination or a luminous body. Preferably, a diffusereflectance of visible rays at 555 nanometers is not less than 0.8. Thisis because the wavelength range which, in particular, contributes tobrightness in the wavelength range of visible rays is generally known tobe from 550 to 555 nanometers. In the present invention, a diffusereflectance is a spectral reflectance factor described in JIS Z8722.2(2), and is also referred to as spectral reflectance. It can bemeasured according to JIS Z 8722.4. An increase of a diffuse reflectanceof a visible light reflective coat is achieved by adding a visible lightreflective pigment to the coat.

Publicly well-known pigments can be used as the visible light reflectivepigment, examples of which include aluminum, silver, titanium oxide,barium sulfate, zinc oxide, and the like. Among them, titanium oxide ispreferred when added in the coat. Because the refractive index of atitanium oxide is high, the diffuse reflection effect becomes higherwhen a titanium oxide is added in the coat.

A content of a titanium oxide is preferably 40 to 250 parts by weightbased on 100 parts by weight of a solid content of a binder in the coat.The titanium oxide content of less than 40 parts by weight is notpreferable because a visible light reflection function does not improve.The titanium oxide content of more than 250 parts by weight is also notpreferable because there are faults such as thickening or gelling of acoating material of the coat. The titanium oxide content is morepreferably 65 to 150 parts by weight. However, it is necessary to selectthe titanium oxide content suitably because a specific gravity of aresin varies with types of the binder resin, and a range of optimumcontent of a titanium oxide also varies a little.

Publicly known titanium oxides can be used as a titanium oxide used inthe present invention. Examples of a titanium oxide include “TIPAQUE™”by Ishihara Sangyo Kaisha, Ltd., and “TITANIX™” by Tayca Corp. However,there are a rutile type and an anatase type among publicly knowntitanium oxides, and a rutile type is preferably used for the presentinvention. An anatase type has a possibility of decomposing a binder ofthe coat, because it has larger photocatalysis than a rutile type does.A surface of a titanium oxide may be treated with Al, Si, Zr, organicsubstances, or the like for purposes of reducing photocatalysis,improving a pigment dispersibility, or improving a weather resistance ofa pigment.

As for a thickness of the visible light reflective coat, a thicker oneis preferred because it improves a visible light reflectance, but a toothick coat is not preferable because it reduces the coating workability.Because an optimum thickness varies also with types of coating materialbinder, it cannot generally be specified, but the thickness ispreferably 10 to 50 micrometers.

A total emissivity of the heat absorptive coat in the range of wavenumber of 600 to 3,000 cm⁻¹ measured at a certain temperature within therange of from 80 to 200 degrees centigrade is not less than 0.70.Because rays having a wave number of less than 600 cm⁻¹ or more than3,000 cm⁻¹ have a very small influence on heat, an emissivity includingrays having such a wave number is inappropriate. Moreover, a heatabsorptive function declines when the total emissivity is less than 0.7.

Hereinafter, common knowledge about heat absorption is described. It isknown that heat is a part of electromagnetic radiations emitted from anobject and that when heat radiation rays enter an object, a part of themreflects, a part of them transmits, and the remaining part of them isabsorbed. See, for example, Nishikawa and Fujita,“Mechanical-engineering basic lecture; Electrothermics” published byRikogakusha Publishing Co., Ltd. When heat radiation rays go into ametal sheet, because heat radiation rays scarcely pass through the metalsheet, the heat radiation rays either reflect or are absorbed. When heatradiation rays generated from an illuminator or a light signal-emittinginstrument go into a light reflector surface, if most of heat radiationrays incident on the surface reflect, the temperature of the instrumentwill rise, and on the other hand, if most of heat radiation rays areabsorbed on the light reflector surface, the temperature of theinstrument will fall.

A reflection method using an infrared spectrophotometer is well known asa method of examining the reflectance of heat radiation rays incident toa surface of a metal sheet and the like. When the reflectance ismeasured by this method, however, if the roughness on a surface of ametal sheet is coarse, the incident heat radiation rays will reflectdiffusively and, therefore, it is difficult to obtain a highly preciseabsorption coefficient. According to Kirchhoff's law on heat radiation,at a constant temperature, an absorptivity and an emissivity of anobject are the same. See, for example, Nishikawa and Fujita,“Mechanical-engineering basic lecture; Electrothermics” published byRikogakusha Publishing Co., Ltd.

Furthermore, the inventors found out that it is preferred that the heatabsorptive coat comprises 10 to 150 parts by weight of a heat absorptivepigment, based on 100 parts by weight of a solid content of the binderof the coat, in order to improve the emissivity of the heat absorptivecoat. A heat absorptive pigment content of less than 10 parts by weightis not preferable because the emissivity tends to become less than 0.7.A heat absorptive pigment content of more than 150 parts by weight isalso not preferable because a storage stability of a coating material ofthe coat is bad.

Publicly known heat absorptive pigments can be used as the heatabsorptive pigment, examples of which include aniline black,polymethylene dyes, tris azo dye amine salts, cyanine dyes or metalcomplexes thereof, anthraquinone-based pigments, phthalocyanine-basedpigments, iron oxides, carbons, and the like. Among these publicly knownheat absorptive pigments, carbon is preferred because it radiatesinfrared rays in a broad range of wave number.

Publicly known carbons, such as carbon black, charcoal, graphite, can beused as the carbon. A carbon to be added is preferably a mixture of acarbon having a particle size of less than 0.1 micrometers (hereinafterreferred to as “a small particle size carbon”) and a carbon having aparticle size of from 0.1 (inclusive) to 30 (exclusive) micrometers(hereinafter referred to as “a large particle size carbon”). A contentof the small particle size carbon is preferably from 1 to 20 parts byweight, and a content of the large particle size carbon is preferablyfrom 1 to 140 parts by weight, and a total content of the small andlarge particle size carbons is preferably 10 to 150 parts by weight,based on 100 parts by weight of a solid content of the binder. Althougha minimum particle size of the small particle size carbon is notlimited, it is not preferable that a maximum particle size thereof isnot less than 0.1 micrometer because interstices between carbonparticles tend to be formed and it becomes difficult to play the role ofa small particle size carbon. It is not preferable that a content of thesmall particle size carbon is less than 1 part by weight because thereis a possibility of an inferior effect for opacifying the metal sheetand of an inferior heat absorptivity. It is also not preferable that acontent thereof is more than 20 parts by weight because there is apossibility that a viscosity of the coating liquid may become high orthe coating liquid may be gelled as time passes. It is not preferablethat the large particle size carbon has a particle size of less than 0.1micrometer because it does not play a role as a large particle sizecarbon and it behaves in the same manner as a small particle size carbondoes. It is not preferable that the large particle size carbon has aparticle size of not less than 30 micrometers because there is apossibility that applicability may decline when applying a coatingliquid comprising such a carbon or the appearance of a coat aftercoating becomes bad. It is not preferable that a content of the largeparticle size carbon is less than 1 part by weight because there is apossibility that a heat absorptivity may be inferior. It is also notpreferable that a content thereof is more than 140 parts by weightbecause there is a possibility that the coat may become weak and theworkability of the coat may be inferior. Furthermore, it is notpreferable that a total content of the small and large particle sizecarbons is less than 10 parts by weight because there is a possibilityof an inferior heat absorptivity. It is also not preferable that thetotal content is more than 150 parts by weight, because there is apossibility that the coat becomes weak and then the formability of thecoat is inferior or there is a possibility that the coating liquidthickens and then the coating workability is inferior.

A thickness of the heat absorptive coat is not limited, but ispreferably not less than 1 micrometer. It is not preferred that athickness of the heat absorptive coat is less than 1 micrometer becausethe heat absorptivity may be inferior. Although a maximum thicknessthereof is not limited, too much thickness tends to cause poorappearance, such as coating unevenness. Therefore, it is necessary toselect the thickness suitably as required. Generally, the thickness ispreferably less than 100 micrometers.

In addition to a heat absorptive pigment, the heat absorptive coatpreferably comprises from 1 to 50 parts by weight of conductive metalpowder, based on 100 parts by weight of the solid content of the binder,as a conductive pigment to make the precoated metal sheet conductive. Itis preferable that the heat absorptive coat is conductive because thelight reflector can secure grounding, and static electricity is hardlygenerated in the light reflector and, therefore, dust is hardlyattached. It is not preferable that a content of the metal powder isless than 1 part by weight because the obtained conductivity is small.It is also not preferable that a content thereof is more than 50 partsby weight because the formability of the coat tends to decline. Examplesof the conductive metal powder used include, but are not limited to,aluminum, nickel, stainless steels, copper, silver, magnesium, zinc,tin. The shape of metal powder is not limited, but must be selectedsuitably because the degree of conductivity may vary with shapes andsome shapes hinder the heat absorptivity. As far as the inventors know,a combination of a flaky metal and a chain-form metal is more preferred.A chain-form metal is preferably used because an area reflecting heat inthe coat becomes small and the heat absorption is hard to prevent.However, it is better to combine a chain-form metal with a flaky metalbecause there is a possibility that conductivity is inferior when usingonly a chain-form metal. A weight ratio of a flaky metal to a chain-formmetal is preferably in the range between 0.1/1 and 6/1 because a heatabsorptivity and conductivity are excellent. Because a flaky metal has alarge area reflecting heat in the coat, there is a possibility ofpreventing heat absorption. Therefore, the conductivity is inferior whenthe weight ratio of a flaky metal to a chain-form metal may be less than0.1/1. There is a possibility that the heat absorptivity may be inferiorwhen the ratio is more than 6/1. Among metals, nickel is preferredbecause it hardly prevents heat absorption of a heat absorptive pigment,compared with other metals.

A binder constituting the visible light reflective coat or the heatabsorptive coat may be a resin, or a publicly known coating binder forinorganic coats formed by a sol gel process, inorganic and organiccomposite coats formed by a sol gel process, or the like. It ispreferred to use a resin in such a form as a coating material due toeasy handling and simple method of coat formation. Publicly known resinscan be used as the resin, examples of which include polyester resins,urethane resins, acrylic resins, epoxy resins, melamine resins, vinylchloride resins, fluororesins, and the like. The resin may be eitherthermoplastic or thermosetting. Several types of these resins may beused together as required. Among these resins, a used resin is notlimited, but is necessary to be selected suitably as required becausethe performances, such as workability, adhesion, and hardness, of thecoat vary with the type, molecular weight, or glass transitiontemperature (Tg) of resins. When using a resin which is cured by acrosslinking agent, the performances, such as workability, adhesion, andhardness, of the coat vary with a type of a crosslinking agent and anaddition amount thereof, and a type of a catalyst used in crosslinkingreaction and an addition amount thereof, which are not limited but arenecessary to be selected suitably as required. The resin may be solid,water-soluble, or water-dispersed emulsion. When a solid resin is used,it can be thermofused, dissolved in an organic solvent, or pulverizedinto powder in advance. Ultraviolet (UV) curable resins and electronbeam (EB) curable resins may be also used. Any of these resins may be acommercially available one.

According to the knowledge which the inventors gained until now,solvent-based melamine-curable polyester binders, solvent-basedisocyanate-curable polyester binders, and water-dispersed acrylicemulsion binders are preferred as the binder. Particularly preferredexamples of the binder include, but are not limited to, the following.

As to a solvent-based melamine-curable polyester binder, a numberaverage molecular weight of a polyester resin is preferably from 2,000to 30,000, a Tg of a polyester resin is preferably from −10 to 70degrees centigrade, and an addition amount of a melamine resin ispreferably from 5 to 70 parts by weight based on 100 parts by weight ofthe polyester resin. It is not preferable that the molecular weight ofthe polyester resin is less than 2,000 because the workability of thecoat declines. It is also not preferable that the molecular weight ismore than 30,000 because a viscosity of a solution of the resindissolved in a solvent is too high. It is not preferable that a Tg ofthe polyester resin is less than −10 degrees centigrade because a coatcannot be formed. It is also not preferable that the Tg is more than 70degrees centigrade because the coat is too hard and the workabilitydeclines. It is not preferable that the addition amount of the melamineis less than 5 parts by weight, based on 100 parts by weight of thepolyester resin, because the coat is uncured. It is also not preferablethat the addition amount is more than 70 parts by weight because thecoat is too hard and the workability declines. A polyester resin to beused may be a commercially available one, examples of which include“VYLON™” by Toyobo Co., Ltd. and “Desmophen™” by Sumitomo Bayer UrethaneCo., Ltd. A melamine resin to be used may also be a commerciallyavailable one, examples of which include “CYMEL™” and “MYCOAT™” byMitsui Cytec, Ltd., and “BECKHAMIN™” and “SUPERBECKHAMIN™” by DainipponInk & Chemicals, Inc.

As to a solvent-based isocyanate-curable polyester binder, a numberaverage molecular weight of a polyester resin is preferably from 2,000to 30,000, a Tg of a polyester resin is preferably from −10 to 70degrees centigrade, and an addition amount of isocyanate is preferablysuch that a value of [NCO group of isocyanate in equivalents]/[OH groupof polyester resin in equivalents] is from 0.8 to 1.2. When the value of[NCO group of isocyanate in equivalents]/[OH group of polyester resin inequivalents] is less than 0.8 or more than 1.2, the coat tends to beuncured when the coat is formed. It is not preferable that the molecularweight of the polyester resin is less than 2,000 because the workabilityof the coat declines. It is also not preferable that the molecularweight is more than 30,000 because a viscosity of a solution of theresin dissolved in a solvent is too high. It is not preferable that a Tgof the polyester resin is less than −10 degrees centigrade because acoat cannot be formed. It is also not preferable that a Tg of thepolyester resin is more than 70 degrees centigrade because the coat istoo hard and the workability declines. A polyester resin to be used maybe a commercially available one, examples of which include “VYLON™” byToyobo Co., Ltd. and “Desmophen™” by Sumitomo Bayer Urethane Co., Ltd.An isocyanate to be used may be also a commercially available one,examples of which include “Sumidur™” and “Desmodur™” by Sumitomo BayerUrethane Co., Ltd., and “Takenate™” by Mitsui Takeda Chemicals, Inc.

A water-dispersed acrylic emulsion binder to be used may also be apublicly known one or a commercially available one. When awater-dispersed acrylic emulsion binder is used, a publicly known highlyadhesive resin such as an epoxy resin may be added to the binder. Thetype and content of the epoxy resin can be selected suitably, if needed,because they have an influence on the performance of the coat. Awater-based resin such as a water-dispersed acrylic resin is morepreferable because the coating workability is high, there is no problemof releasing a volatile organic solvent into the atmosphere, and thereare no need of a buildup of an exhaust duct and a combustion equipmentof a volatile organic solvent in a coater.

When the visible light reflective pigment added in the visible lightreflective coat of the precoated metal sheet according to the presentinvention is a titanium oxide, the binder resin in the visible lightreflective coat preferably comprises a fluororesin because thereflectivity is improved. Because a fluororesin has a lower refractiveindex than any other publicly known resins, when a fluororesin iscombined with a titanium oxide having a high refractive index, arefractive index difference between the binder resin and the titaniumoxide pigment is large, and light reflects more easily on the interfacesbetween them.

A fluororesin to be used may be a publicly known one such astrifluoroethylene resins, tetrafluoroethylene resins, vinylidenefluoride resins, and the like. The resin may be a homopolymer or acopolymer with another resin monomer. A fluororesin blended with anotherresin may be used as a fluororesin-containing binder resin. However, acoat having a high fluorine concentration is preferable. It is morepreferable that a trifluoroethylene resin is used because a fluorineconcentration in the coat is high, and it is easy to prepare a coatingmaterial. In the present invention, a trifluoroethylene resin is definedas a resin comprising a poymer having a repeating unit —CF₂—CFX—,wherein X is hydrogen or a halogen other than fluorine. Examples of atrifluoroethylene resin include a poly(chlorotrifluoroethylene). Thebinder resin comprising a fluororesin may be a commercially availablefluorine-based coating resin, examples of which include “Kynar™” serieswhich are vinylidene fluoride homopolymers by ATOFINA Chemicals, Inc.,and “LUMIFLON™” series which are copolymers of trifluoroethylene resinand another resin by Asahi Glass Co., Ltd. When a vinylidene fluoridehomopolymer is used, it is commonly blended with an acrylic resin beforeuse. These resins may be crosslinked, if needed, by a publicly knowncrosslinking agent such as isocyanate or a melamine resin. An isocyanateto be used may be a commercially available one, examples of whichinclude “Sumidur™” and “Desmodur™” by Sumitomo Bayer Urethane Co., Ltd.,and “Takenate™” by Mitsui Takeda Chemicals, Inc. A melamine resin to beused may be a commercially available one, examples of which include“Cymel™” and “MYCOAT™” by Mitsui Cytec, Ltd., and “BECKHAMIN™” and“SUPERBECKHAMIN™” by Dainippon Ink & Chemicals, Inc. It is not necessaryto use a crosslinking agent. It is preferable that an amount of acrosslinking agent added is not more than 20 parts by weight based on100 parts by weight of the total resins including a fluororesin becausea fluorine concentration in the coat becomes higher and the visiblelight diffuse reflectance is also improved. It is more preferred that atrifluoroethylene resin having a hydroxyl value of not more than 10mg-KOH/g is used and an amount of a crosslinking agent added is not morethan 20 parts by weight, based on 100 parts by weight of the totalresins including the trifluoroethylene resin, because the diffusereflectance of visible rays is improved. This is because, when thehydroxyl value is not more than 10 mg-KOH/g, the coat is crosslinked bya small amount of crosslinking agent, or the coat is formed even if acrosslinking agent is not used, and a fluorine concentration in the coatbecomes high.

The visible light reflective coat or heat absorptive coat can furthercomprise a color pigment, a rust preventing pigment, or a rustpreventive, if necessary, in addition to a titanium oxide, a heatabsorptive pigment, and a conductive pigment. However, when trying tomore improve a visible light reflectance of the visible light reflectivecoat, a coat consisting only of a binder resin and a titanium oxide ismore preferable because the diffuse reflectance of visible light isimproved. If a pigment other than a titanium oxide is added in thevisible light reflective coat, interfaces having a small difference ofrefractive index will occur between a binder resin and a pigment otherthan a titanium oxide, and a visible light diffuse reflectance of thecoat declines. However, from a standpoint of appearance or corrosionprotection, if necessary, a pigment other than a titanium oxide may beadded to the visible light reflective coat.

Publicly known inorganic or organic color pigments are used as the colorpigment. Examples of inorganic color pigments include zinc oxide (ZnO),zirconium oxide (ZrO₂), calcium carbonate (CaCO₃), barium sulfate(BaSO₄), alumina (Al₂O₃), kaolin clay, and iron oxides (Fe₂O₃, Fe₃O₄).

Examples of the rust preventing pigment or rust preventive includepublicly known chromium-containing rust preventive pigments such asstrontium chromate and calcium chromate, and publicly knownchromium-free rust preventing pigments or rust preventives such as zincphosphate, zinc phosphite, aluminum phosphate, aluminum phosphite,molybdates, phosphate/molybdate salts, vanadate/phosphate mixturepigments, silica, and Ca-adsorbed silicas called calcium silicates. Whena base metal of the precoated metal sheet is an easily corrosive metalsuch as a steel sheet or a plated steel sheet, it is preferable that arust preventing pigment or rust preventive is added in order to improvethe corrosion resistance of the precoated metal sheet. Chromium-freerust preventing pigments or rust preventives are more effective if anenvironmental problem in recent years is considered. As a chromium-freerust preventing pigment or rust preventive, either a reagent or acommercially available one may be used. Examples of commerciallyavailable rust preventing pigments include zinc phosphate-based rustpreventing pigments “EXPERT™-NP500” and “EXPERT™-NP530” by Toho GanryoCo., Ltd., zinc phosphite-based rust preventing pigments“EXPERT™-NP1500”, “EXPERT™-NP1530”, “EXPERT™-NP1600” and“EXPERT™-NP1700” by Toho Ganryo Co., Ltd., aluminum triphosphates“K-WHITE” series by Tayca Corporation, molybdate-based pigments orphosphate/molybdate-based pigments “SHER-WHITE” series by theSherwin-Williams Company, fumed silicas “AEROSIL™” series by NipponAerosil Co., Ltd. or Degussa Japan Co., Ltd., colloidal silicas“SNOWTEX™” series by Nissan Chemical Industries, Ltd., calcium ionadsorbed silicas “SHIELDEX™” series by GRACE, and the like. Two or moreof these rust preventing pigments can be used in combination. Amongthese chromium-free rust preventing pigments, a calcium ion adsorbedsilica alone or a combination of a calcium ion adsorbed silica and aphosphate-based rust preventing pigment is preferred because it isexcellent in corrosion resistance and press-formability on the precoatedmetal sheet. A combination of a calcium ion adsorbed silica and aluminumtriphosphate is more preferred.

It is necessary to suitably select a type, an addition amount, and aparticle size of these color pigments, rust preventing pigments, or rustpreventives as required because the coat performances, such as anemissivity, workability, appearance, and corrosion resistance, vary withthem.

Publicly known additives such as leveling agents, pigment dispersants,waxes, delustering agents, and the like can be added, if necessary, tothe heat absorptive coat. However, the visible light reflective coatpreferably does not comprise such an additive because such an additivereduces the diffuse reflectance of visible lights. However, if necessaryfor the coating workability or the coat performances, such an additivemay be added also to the visible light reflective coat. The type orcontent of the additive is not limited, and can be selected suitably asrequired. In particular, a wax is effective in improving the formabilityof the precoated metal sheet, and in preventing the heat absorptive coatfrom cracking, and the like.

A low visible light regular reflectance of a light reflector issometimes preferred, depending on applications of a precoated metalsheet for light reflectors of the present invention. If the regularreflectance of a light reflector is high, the reflected light does notdiffuse and only a specific part becomes bright, or the image of thelight source, such as an electric bulb and a fluorescent lamp, isreflected on the light reflector surface. In a light reflector of aliquid crystal television set, for example, unless light isdiffuse-reflected more uniformly and transmitted to a liquid crystaldisplay, there is a possibility that the light and shade of brightnessmay occur in an image in a liquid crystal display. Light reflectors forsuch an application sometimes require a low regular reflectance ofvisible lights. It is known that a regular reflectance of visible lightshas a negative correlation with a gloss of a surface of the visiblelight reflective coat, and that the lower the gloss is, the lower theregular reflectance becomes. Therefore, one preferred means of reducingthe visible light regular reflectance of the visible light reflectivecoat is the addition of a delustering agent to the visible lightreflective coat. The delustering agent to be used may be a publiclyknown delustering agent, and silicas or silica-based pigments areeffective. Among silica-based pigments, a metal ion adsorbed silica ispreferred because it also improves the corrosion resistance. Publiclyknown silicas can be used as silica for the delustering agent. Examplesthereof include fumed silicas “AEROSIL™” series by Nippon Aerosil Co.,Ltd. or Degussa Japan Co., Ltd., colloidal silicas “SNOWTEX™” series byNissan Chemical Industries, Ltd. and the like. Calcium ion adsorbedsilicas “SHIELDEX™” series by GRACE can be used as the metal ionadsorbed silica. However, unless a low regular reflectance of visiblelight or a low gloss is demanded, it is preferred that the visible lightreflective coat does not comprise a delustering agent and the like andconsists only of a binder resin and a titanium oxide because the diffusereflectance is higher than when it comprises a delustering agent.

In order to form a visible light reflective coat and a heat absorptivecoat on a surface of the metal sheet, the metal sheet can be coated withcomponents, including a binder, of the coat in a publicly known form ofa coating material. Examples of the form include solvent-based coatingmaterials in which a resin is dissolved in a solvent, aqueous coatingmaterials in which an emulsified resin is dispersed in water and thelike, powder coating materials obtained by pulverizing a resin into apowder, slurry powder coating materials in which a pulverized resin isdispersed in water and the like, ultraviolet (UV) curable coatingmaterials, electron beam (EB) curable coating materials, film laminationin which a resin is formed into a film shape and the film is laminated,and melt coating in which a resin is melted and applied. Examples of acoating method include, but are not limited to, roll coating, rollercurtain coating, curtain flow coating, air spray coating, airless spraycoating, brush coating, die coater coating, and other publicly knowncoating methods. Among them, roll coating, roller curtain coating,curtain flow coating, and die coater coating are preferred becausecontinuous process is possible and production efficiency is improved.

A primer coat may be provided under the visible light reflective coat orthe heat absorptive coat for the purpose of rust proofing or masking.Publicly known binders, rust preventing pigments, and color pigments canbe used for the primer coat. Commercially available coating materialsmay be used for the primer coat. The same binders, rust preventingpigments, and color pigments as the above-mentioned ones used for thevisible light reflective coat or heat absorptive coat may be used. Aprimer coat under the visible light reflective coat preferably comprises40 to 250 parts by weight of a visible light reflective pigment,preferably a titanium oxide, based on 100 parts by weight of the solidcontent of the binder because the diffuse reflectance of the visiblelight reflective coat is improved. A thickness of the primer coat ispreferably, but is not limited to, from 1 to 40 micrometers. When thethickness is less than 1 micrometer, there is a possibility that theprimer coat does not play a role such as masking or corrosionresistance. When the thickness is more than 40 micrometers, there is apossibility that the coating workability declines. The same binderresins as those used for the visible light reflective coat or the heatabsorptive coat can be used for the primer coat. Moreover, publiclyknown additives such as color pigments, rust preventing pigments,leveling agents, pigment dispersants, waxes, delustering agents, and thelike can be added, if necessary, to the primer coat as well as to thevisible light reflective coat or the heat absorptive coat. Inparticular, the addition of a rust preventing pigment to the primer coatis preferred because it improves the corrosion resistance of theprecoated metal sheet. A chromium-free rust preventing pigment ispreferably used. Among chromium-free rust preventing pigments, a calciumion adsorbed silica alone or a combination of a calcium ion adsorbedsilica and a phosphate-based rust preventing pigment is preferredbecause it is excellent in corrosion resistance and press-formability ofthe precoated metal sheet. A combination of a calcium ion adsorbedsilica and aluminum triphosphate is more preferred. When a primer coatis provided under the visible light reflective coat, a delustering agentis preferably added in the primer coat in order to reduce a visiblelight regular reflectance of the visible light reflective coat. Publiclyknown delustering agents can be used as a delustering agent in theprimer coat, and silica-based delustering agents and the like arewell-known.

In addition, a surface of the metal sheet is preferably pretreatedbefore coating the visible light reflective coat or the heat absorptivecoat in order to increase the coat adhesion. Examples of such apretreatment include chromate coating treatment, electrolytic chromatetreatment, zinc phosphate treatment, zirconia-based treatment,titania-based treatment, and other publicly known treatment.Non-chromate pretreatment using an organic compound such as a resin,which has been developed in recent years, is preferred because the loadon the environment is reduced. Examples of non-chromate pretreatmentusing an organic compound such as a resin include treatments describedin Japanese Unexamined Patent Publications No. Hei 09-828291, No. Hei10-251509, No. Hei 10-337530, No. 2000-17466, No. 2000-248385, No.2000-273659, No. 2000-282252, No. 2000-265282, No. 2000-167482, or No.2002-266081, and other publicly known treatments. A commerciallyavailable chromate treatment may be used. A type and coating weight ofthe pretreatment need to be suitably selected, if necessary, because theadhesion of the heat absorptive coat and the corrosion resistance of theprecoated metal sheet vary greatly with the type or coating weight.

Publicly known materials can be used as a base metal of the metal sheetof the precoated metal sheet according to the present invention. Thebase metal may be an alloy. Examples of the metal sheet include steelsheets, aluminum sheets, titanium sheets, copper sheets, and the like. Asurface of the metal sheet may be plated, for example, with zinc,aluminum, copper, or nickel, as well as alloys. Examples of a steelsheet used as the metal sheet include cold rolled sheet steels, hotrolled sheet steels, hot dip zinc coated steel sheets, electrogalvanizedsteel sheet, hot dip alloyed galvanized steel sheets, aluminum-platedsteel sheets, aluminum-zinc alloyed plated steel sheets, stainless steelsheets, and other publicly known steel sheets and plated steel sheets.

A surface roughness Ra of the metal sheet or plated metal sheet ispreferably 0.05 to 1.8 micrometers because the diffuse reflectance isimproved. When visible rays go into a surface of the visible lightreflective coat, visible rays transmitting the visible light reflectivecoat without reflected are reflected on a surface of the base metalsheet under the coat. The inventors found that, when the surfaceroughness of the base metal sheet was much smaller than the visible raywavelengths (the wavelength region of visible rays is usually said to be380 to 780 nanometers), visible rays incident on the base metal surfaceare hardly diffuse-reflected but are easily regular-reflected. On theother hand, when the surface roughness of the base metal sheet is muchlarger than the wavelengths of visible rays, visible rays incident onthe base metal surface enter the interstices between the unevenness onthe surface of a base metal and are easily absorbed by the base metal.Therefore, it is not preferable that a surface roughness Ra of the metalsheet or plated metal sheet which is the base metal is less than 0.05micrometers because it is hard to diffuse-reflect visible rays. It isalso not preferable that the Ra is more than 1.8 micrometers becausevisible rays passing the visible light reflective coat without reflectedand reaching the metal sheet or plated metal sheet which is a base metalare easy to absorb by the base metal surface.

The metal sheet may be subjected to an usual treatment, such as hotwater rinsing, alkaline degreasing, and acid pickling, prior toperforming the before-coating pretreatment. A sheet steel or platedsteel sheet is preferably used as the metal sheet because the formingworkability of the precoated metal sheet is improved.

A reflector production efficiency improves if the reflector is producedby forming a precoated metal sheet of the present invention. A reflectorcan be produced by a publicly known forming method, examples of whichinclude blanking, bending, deep drawing, stretch forming, roll forming,and other forming methods.

In an electric or electronic apparatus comprising a precoated metalsheet according to the present invention, because the precoated metalsheet has a high diffuse reflectance of visible rays as well as anexcellent heat absorptivity, the light of illumination or light signalbecome brighter and the temperature in the apparatus declines and,therefore, electronic circuits of a control board and the like providedin the apparatus can work efficiently and stably. Examples of theelectric or electronic apparatus include illuminators, audiovisualequipment, mobile computing devices, plasma displays, liquid crystaltelevision sets.

EXAMPLES

The methods of preparing heat absorptive coating materials and visiblelight reflective coating materials used in the experiments will beexplained in detail below.

A commercially available organic solvent soluble amorphous polyesterresin “VYLON™ GK140” having a number average molecular weight of 13,000and a Tg of 20 degrees centigrade by Toyobo Co., Ltd. (hereinafterreferred to as the polyester resin) was dissolved in an organic solventconsisting of 50 percent by weight of Solvesso™ 150 and 50 percent byweight of cyclohexanone.

Subsequently, 15 parts by weight of a commercially availablehexamethoxymethylmelamine “CYMEL™ 303” by Mitsui Cytec, Ltd. and 0.5parts by weight of a commercially available acid catalyst “Catalyst6003B” by Mitsui Cytec, Ltd., based on 100 parts by weight of the solidcontent of the polyester resin, were added to the polyester resindissolved in the organic solvent. The resultant mixture was agitated toobtain a melamine curable polyester-based clear coating material, whichis hereinafter referred to as the polyester/melamine-based coatingmaterial.

In order to examine the effect of resins, the above-mentioned polyesterresin dissolved in the organic solvent was blended with a commerciallyavailable HDI (hexamethylene diisocyanate)-based blocking isocyanate“Sumidur™ BL3175” by Sumitomo Bayer Urethane Co., Ltd. at a value [NCOgroup of isocyanate in equivalents]/[OH group of polyester resin inequivalents] of 1.0, and further 0.05 parts by weight of a reactioncatalyst “TK-1” by Mitsui Takeda Chemicals, Inc., based on 100 parts byweight of the solid content of the resin, was added to obtain anisocyanate curable polyester-based clear coating material, which ishereinafter referred to as the polyester/isocyanate-based coatingmaterial.

In order to further examine the effect of resins, a commerciallyavailable trifluoroethylene-based resin “LUMIFLON™ LF552” having anumber average molecular weight of 12,000 and a Tg of 20 degreescentigrade by Asahi Glass Co., Ltd. was blended with a commerciallyavailable HDI (hexamethylene diisocyanate)-based blocking isocyanate“Sumidur™ BL3175” by Sumitomo Bayer Urethane Co., Ltd. at a value [NCOgroup of isocyanate in equivalents]/[OH group of polyester resin inequivalents] of 1.0, and further 0.05 parts by weight of a reactioncatalyst “TK-1” by Mitsui Takeda Chemicals, Inc., based on 100 parts byweight of the solid content of the resin, was added to obtain afluorine-based clear coating material, which is hereinafter referred toas the fluorine-based coating material.

Subsequently, various pigments were added to the obtained clear coatingmaterials to prepare visible light reflective coating materials, heatabsorptive coating materials, and primer coating materials.

The details of the prepared coating materials are described below.

[Visible Light Reflective Coating Materials]

A titanium oxide “TIPAQUE CR95” by Ishihara Sangyo Kaisha, Ltd. wasadded to the clear coating materials and was agitated to obtain visiblelight reflective coating materials, which are sometimes referred tosimply as “reflective coating materials.” The details of types of usedclear coating materials and the content of the titanium oxide are shownin Table 1. The content of the titanium oxide in Table 1 is expressed byparts by weight of the titanium oxide based on 100 parts by weight ofthe resin solid content of the clear coating material. TABLE 1 CoatingContent of Material No. Coating Material Titanium Oxide NoteReflective-I-1 polyester/isocyanate-based 120 — Reflective-I-2polyester/melamine-based 120 — Reflective-I-3 polyester/melamine-based65 — Reflective-I-4 polyester/melamine-based 30 — Reflective-I-5polyester/melamine-based 300 a) Reflective-I-6 fluorine-based 100 —Note:a) Coating was difficult due to thickening of coating material.

[Heat Absorptive Coating Materials]

Heat absorptive coating materials were obtained by adding a carbon tothe clear coating materials and agitating them.

In this experiment, a carbon black “TOKABLACK #7350F” by Tokai CarbonCo., Ltd. was used as the small particle size carbon. “Bincho CharcoalPowder” having a maximum particle diameter of 5 micrometers sold byCooperative Association LATEST and a carbon having an average particlediameter to 20 micrometers obtained by pulverizing a commerciallyavailable reagent graphite and classifying with a sieve were used as thelarge particle size carbon. A conductive pigment consisting of a mixtureof 6 parts by weight of a commercially available flaky metal nickel and1 part by weight of a commercially available chain-form metal nickel wasadded when necessary.

The details of the prepared heat absorptive coating materials are shownin Table 2. The contents of these additives in Table 2 are expressed byparts by weight of the additive based on 100 parts by weight of theresin solid content of the clear coating material. TABLE 2 Small LargeParticle Particle Conductive Coating Material No. Coating Material SizeCarbon Size Carbon Pigment Note Heat Adsorptive-I-1polyester/isocyanate-based 15 — — — Heat Adsorptive-I-2polyester/melamine-based 15 — — — Heat Adsorptive-I-3polyester/melamine-based 50 — — a) Heat Adsorptive-I-4polyester/melamine-based 100 — — a) Heat Adsorptive-I-5polyester/melamine-based 150 — — a) Heat Adsorptive-I-6polyester/melamine-based 0 50 — — Heat Adsorptive-I-7polyester/melamine-based 5 45 — — Heat Adsorptive-I-8polyester/melamine-based 15 35 — — Heat Adsorptive-I-9polyester/melamine-based 15 — 5 — Heat Adsorptive-I-10polyester/melamine-based 15 — 50 — Heat Adsorptive-I-11polyester/melamine-based 5 — — — Heat Adsorptive-I-12polyester/melamine-based 250 — — b) Heat Adsorptive-I-13polyester/melamine-based 10 240 — b)Note:a) Coating applicability was bad due to thickening of coating material.b) Coating was difficult due to thickening of coating material.

[Primer Coating Materials]

Chromate-free primer coating materials were prepared by adding 20 partsby weight of chromate-free rust preventing pigment “SHIELDEX C303” byGRACE and 40 parts by weight of titanium oxide “TIPAQUE™ CR95” byIshihara Sangyo Kaisha, Ltd. as a visible light reflective pigment,based on 100 parts by weight of the solid content of the resin, to apolyester-based clear coating material FLC641 by Nippon Paint Co., Ltd.and then agitating the resultant mixture. Moreover, the FLC641EU primerwhich is a polyester-based primer coating material sold by Nippon PaintCo., Ltd. was also used as a commercially available chromate-basedprimer.

The method for preparing a precoated metal sheet used in the experimentwill be explained in detail below.

A metal sheet having a thickness of 0.6 millimeters was alkali-degreasedat 60 degrees centigrade in an aqueous solution containing 2 percent byweight of a commercially available alkali degreasing agent “FC4336” byNihon Parkerizing Co., Ltd., and then was rinsed with water and dried.Subsequently, a conversion treatment liquid was applied on the degreasedmetal sheet using a roll coater, and then the sheet was dried with hotair at a peak metal temperature of 60 degrees centigrade.

The following metal sheets were used in this experiment. Roughnesses ofthese metal sheets were adjusted by rolling the metal sheets with areduction roll in order to make the roughnesses of the metal sheetsalmost the same.

EG: a commercially available electrogalvanized steel sheet(Electroplated zinc weight: 20 g/m² on one side, Material: SECE (JISG3313)), Surface roughness Ra: 0.9 micrometers)

AL sheet: a commercially available aluminum plated steel sheet (Aluminumcoating weight: 60 g/m² on one side, Material: SALE (JIS G3314), Surfaceroughness Ra: 1.0 micrometer)

GL: a commercially available 55 percent aluminum-zinc plated steel sheet(Plating weight: 90 g/m² on one side, Material: SGLCD (JIS G3321),Surface roughness Ra: 0.9 micrometers)

Aluminum sheet: a commercially available aluminum sheet (Material: 1100(JIS H4000), Surface roughness Ra: 0.8 micrometers)

A commercially available chromate treatment “ZMI1300AN” by NihonParkerizing Co., Ltd. (hereinafter referred to as the chromatetreatment) and a commercially available non-chromate conversiontreatment “CT-E300” by Nihon Parkerizing Co., Ltd. (hereinafter referredto as the non-chromate treatment) were used as a conversion treatment inthis experiment. Both surfaces of a metal sheet were conversion-treatedwith a roll coater, and then were dried at a peak metal temperature of60 degrees centigrade. The coating weight of the chromate treatment was50 milligrams of Cr per square meter. The coating weight of thenon-chromate treatment was 150 milligrams of the total coating weightper square meter.

Subsequently, the primer coating material was applied on one surface ofthe conversion-treated metal sheet, and the heat absorptive coatingmaterial described in Table 2 was applied on the other surface with aroll coater, and then dried and cured at a peak metal temperature (PMT)of 210 degrees centigrade in an induction heating furnace using hot airin combination. Subsequently, the visible light reflective coatingmaterial described in Table 1 was applied on the surface coated with theprimer coating material by a roller curtain coater, and then dried andcured at a peak metal temperature (PMT) of 230 degrees centigrade in aninduction heating furnace using hot air in combination. Precoated metalsheets without a primer coat were also prepared as required. Thethickness of the primer coat was 10 micrometers when dried, thethickness of the visible light reflective coat was 20 micrometers whendried, and the thickness of the heat absorptive coat was 5 micrometerswhen dried. The details of the precoated metal sheets (PCM) prepared areshown in Table 3. TABLE 3 Coating material for visible Coating materialfor heat Conversion light reflective coat side adsorptive coat side PCMNo. Metal sheet treatment Primer coat Top coat Top coat PCM-I-1 EGNon-chromate Chromate-free Reflective-I-1 Heat Adsorptive-I-2 PCM-I-2 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-2 PCM-I-3 EGNon-chromate Chromate-free Reflective-I-3 Heat Adsorptive-I-2 PCM-I-4 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-1 PCM-I-5 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-3 PCM-I-6 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-4 PCM-I-7 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-5 PCM-I-8 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-6 PCM-I-9 EGNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-7 PCM-I-10EG Non-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-8PCM-I-11 EG Non-chromate Chromate-free Reflective-I-2 HeatAdsorptive-I-9 PCM-I-12 EG Non-chromate Chromate-free Reflective-I-2Heat Adsorptive-I-10 PCM-I-13 EG Non-chromate Reflective-I-2Reflective-I-2 Heat Adsorptive-I-2 PCM-I-14 EG Chromate Chromate-basedReflective-I-2 Heat Adsorptive-I-2 PCM-I-15 EG Non-chromateChromate-free Reflective-I-2 Heat Adsorptive-I-2 PCM-I-16 AL sheetNon-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-2 PCM-I-17GL Non-chromate Chromate-free Reflective-I-2 Heat Adsorptive-I-2PCM-I-18 Aluminum sheet Non-chromate Chromate-free Reflective-I-2 HeatAdsorptive-I-2 PCM-I-19 EG Non-chromate Chromate-free Reflective-I-6Heat Adsorptive-I-2 PCM-I-20 EG Non-chromate Chromate-freeReflective-I-4 Heat Adsorptive-I-2 PCM-I-21 EG Non-chromateChromate-free Reflective-I-2 Heat Adsorptive-I-11

Test methods for evaluating the precoated metal sheets prepared will beexplained in details below.

1) Visible Ray Diffuse Reflectance of Visible Light Reflective Coat

Visible ray diffuse reflectance of a visible light reflective coatsurface of the prepared precoated metal sheet was measured in awavelength range of from 400 to 700 nanometers using a spectrophotometer“UV265” by Shimadzu Corp. with an integrating sphere reflectiveattachment being additionally attached, and the integral value of theobtained wavelength-reflectance curve was determined. Moreover, avisible ray diffuse reflectance in the wavelength of 555 nanometerswhich contributes to brightness most was also measured. A reference usedwas barium sulfate made by Merck & Co., Inc. which is a white specimenaccording to German DIN standard (DIN5033), and the diffuse reflectanceof each coat was determined when the diffuse reflectance of thereference was defined as 1.00.

2) Gloss Of Visible Light Reflective Coat

A specular gloss of a visible light reflective coat surface of aprecoated metal sheet was measured at an incidence angle of 60 degreesand an acceptance angle of 60 degrees according to JIS K 5400.7.6.

3) Emissivity of Metal Sheet at Heat Absorptive Coat Side

An infrared emission spectrum of the prepared precoated metal sheet wasmeasured in a wave number range of from 600 to 3000 cm⁻¹ at a sheettemperature of 80 degrees centigrade using a Fourier transform infraredspectrophotometer “VALOR-III” by Jasco Corp., and was compared with anemission spectrum of a standard black body to determine a totalemissivity of the metal sheet. In this connection, an iron sheet whichwas spray-coated with “THI-1B Black Spray” manufactured by Okitsumo Inc.and sold by Tasco Japan Inc. at a coat thickness of 30±2 micrometers wasused as the standard black body. The emissivity was measured on the heatabsorptive coat surface of the precoated metal sheet prepared.

4) Illumination Of Illuminator

A sketch of an instrument used for measuring illumination is shown inFIG. 2. A commercially available fluorescent illuminator 12 was attachedin a wooden case 11. A sensor 14 of a commercially availableilluminometer was placed at a distance of 30 centimeters from afluorescent lamp 13, and then illumination was measured. An lightreflector 15 originally attached to the fluorescent illuminator 12(hereinafter referred to as the conventional light reflector) wasremoved. A light reflector 15 having the same shape as that of theconventional light reflector 15 was formed using each of the preparedprecoated metal sheets. Illuminations were measured when each formedlight reflector 15 was attached to the illuminator 12 as well as whenthe conventional light reflector 15 was attached to the illuminator 12.A 16-watt fluorescent lamp 13 was used in this experiment. Eachprecoated metal sheet was evaluated by comparing the illuminationmeasured when a light reflector 15 made of the precoated metal sheet wasattached with the illumination measured when the conventional lightreflector 15 was attached as follows:

“Very good” when the illumination rate is not less than 110 percent,

“Good” when the illumination rate is not less than 103 percent and lessthan 110 percent, and

“Bad” when the illumination rate is less than 103 percent,

wherein the illumination rate is defined as [illumination measured whena light reflector made of a precoated metal sheet wasattached]/[illumination measured when the conventional light reflectorwas attached]×100.

5) Bend Test of Coat of Precoated Metal Sheet (Workability)

A precoated metal sheet prepared was bent in close contact at a bendangle of 180 degrees at 20 degrees centigrade, and the damaged conditionof the coat at the bent portion was observed with a magnifying lens. Theworkability was evaluated according to the following criterion. Thistest employed 3T bending in which the precoated metal sheet specimen wasbent in close contact at a bending angle of 180 degrees while threesheets having the same thickness as the precoated metal sheet to beevaluated are inserted inside. This test was performed on both thevisible light reflective coat side and the heat absorptive coat side ofa precoated metal sheet.

“Good” when there is no damage in the coat,

“Normal” when the coat is damaged partially, and

“Bad” when the coat is violently damaged all over the bent portion.

6) Cupping Formability of Precoated Metal Sheet

A cupping test was performed on the conditions of a punch diameter of 50millimeters, a punch shoulder R (radius of a punch shoulder) of 3millimeters, a dice shoulder R (radius of the shoulder of a dice) of 3millimeters, and a draw ratio of 2.1. At the time of the cupping test, apress test was performed without applying a press oil to the precoatedmetal sheet surface and with the visible light reflective coat surfacebeing outside of the cup. The formability of a precoated metal sheet wasevaluated as follows:

“Very good” when the precoated metal sheet can be formed into thedesignated shape completely without fracture of the base metal in themiddle of forming, and no damage of the coat is visually observed.

“Good” when the base metal is fractured in the middle of forming theprecoated metal sheet, but neither clear coat peeling nor coat damage isvisually observed at the formed portion.

“Bad” when clear coat peeling or coat damage is visually observedregardless of the base metal being fractured in the middle of formingthe precoated metal sheet.

7) Corrosion Resistance of Precoated Metal Sheet

A method of evaluating a corrosion resistance of the surface isdescribed below.

A cut crack is made in the visible light reflective coat surface of theprecoated metal sheet prepared, and thereafter a salt spray test wasperformed according to the method described in JIS K 5400.9.1. Saltwater was sprayed on the surface having a cut crack. Test time was 120hours. The width of coat blister from the cut crack on the surface wasmeasured and the corrosion resistance was evaluated as follows:

“Good” when the blister width is not more than 3 millimeters on oneside,

“Normal” when the blister width is less than 5 millimeters on one side,and

“Bad” when the blister width is more than 5 millimeters on one side.

8) Conductivity of Heat Absorptive Coat of Precoated Metal Sheet

A conductivity of a heat absorptive coat of the precoated metal sheetprepared was measured. An electric resistivity of a surface of a heatabsorptive coat of the precoated metal sheet was measured by the fourprobe method using a resistivity meter “Loresta-EP/MCP-T360” by MitsuiChemicals, Inc., and the conductivity was evaluated according to thefollowing criterion:

“Good” when the electric resistivity is less than 0.1×10⁻² ohms,

“Normal” when the electric resistivity is not less than 0.1×10⁻² ohmsand less than 1.0×10⁻¹ ohms, and

“Bad” when the electric resistivity is not less than 1.0×10⁻¹ ohms.

Details of the evaluation results are given below.

Table 4 shows the evaluation results. In this connection, a reflectivecoating material I-5 (see Table 1) and heat absorptive coating materialsI-12 and I-13 (see Table 2) among the prepared coating materials werethickened and solidified due to too much content of titanium oxide orcarbon, and were difficult to coat. Therefore, precoated metal sheetsusing these coating materials could not prepared. TABLE 4 Visible raydiffuse Workability reflectance of visible Gloss of visible Emissivityof Visible light Heat light reflective coat light reflective heatabsorptive Illumination reflective absorptive Cupping Corrosion Conduc-PCM No. 400-700 nm 555 nm coat coat of illuminator coat side coat sideformability resistance tivity PCM-I-1 0.85 0.87 90.3 0.80 Very good GoodGood Very good Good Bad PCM-I-2 0.85 0.87 90.3 0.80 Very good Good GoodVery good Good Bad PCM-I-3 0.73 0.76 90.3 0.80 Good Good Good Very goodGood Bad PCM-I-4 0.85 0.87 90.3 0.80 Very good Good Good Very good GoodBad PCM-I-5 0.85 0.87 90.3 0.90 Very good Good Normal Very good Good BadPCM-I-6 0.85 0.87 90.3 0.90 Very good Good Bad Very good Good BadPCM-I-7 0.85 0.87 90.3 0.90 Very good Good Bad Very good Good BadPCM-I-8 0.85 0.87 90.3 0.72 Good Good Good Very good Good Bad PCM-I-90.85 0.87 90.3 0.80 Very good Good Good Very good Good Bad PCM-I-10 0.850.87 90.3 0.85 Very good Good Good Very good Good Bad PCM-I-11 0.85 0.8790.3 0.80 Good Good Good Very good Good Good PCM-I-12 0.85 0.87 90.30.75 Good Good Good Very good Good Good PCM-I-13 0.88 0.90 90.3 0.70Very good Good Good Very good Normal Bad PCM-I-14 0.82 0.85 90.3 0.80Very good Good Good Very good Good Bad PCM-I-15 0.85 0.87 90.3 0.80 Verygood Good Good Very good Good Bad PCM-I-16 0.85 0.87 90.3 0.80 Very goodGood Good Very good Good Bad PCM-I-17 0.85 0.87 90.3 0.80 Very good GoodGood Very good Good Bad PCM-I-18 0.85 0.87 90.3 0.80 Very good Good GoodGood Good Bad PCM-I-19 0.88 0.90 90.3 0.65 Very good Good Good Very goodGood Bad PCM-I-20 0.60 0.68 90.3 0.80 Bad Good Good Very good Good BadPCM-I-21 0.85 0.87 90.3 0.65 Bad Good Good Very good Good Bad

The illuminators employing the precoated metal sheets of the presentinvention as light reflectors had higher and brighter illumination thanone employing the conventional light reflector. It is unsuitable for thecontent of a titanium oxide in the visible light reflective coat to beless than 65 parts by weight based on 100 parts by weight of the solidcontent of the binder (PCM-I-20) because the visible light reflectanceis less than 0.70 and the illumination is not different from that of theconventional light reflector. It is also unsuitable for the content ofcarbon in a heat absorptive coat to be less than 10 parts by weightbased on 100 parts by weight of the solid content of the binder(PCM-I-21) because the emissivity is less than 0.70 and the illuminationis not different from that of the conventional light reflector. It ispreferable that carbon added to a heat absorptive coat is a combinationof the large particle size carbon and the small particle size carbon(PCM-I-9 and PCM-I-10) because a comparatively large amount of carboncan be added without thickening. It is preferable that a conductivepigment is added to the heat absorptive coat (PCM-I-11 and PCM-I-12)because the conductivity can be given to the heat absorptive coat.However, if the content of a conductive pigment is increased, theemissivity of the heat absorptive coat declines and, therefore, thecontent of the conductive pigment is preferably not more than 50 partsby weight based on 100 parts by weight of the solid content of thebinder. The precoated metal sheet which neither comprises a rustpreventing coat under the visible light reflective coat or the heatabsorptive coat nor contains a rust preventing pigment in these coats(PCM-I-13) has an inferior corrosion resistance. A precoated metal sheettreated by a chromate-based conversion treatment or comprising achromate-based rust preventing pigment in the coat (PCM-I-14) comprisesan environmental impact material and, therefore, a precoated metal sheetneither treated by such a treatment nor comprising such a pigment ispreferred.

It is preferable that the binder resin of the visible light reflectivecoat is a fluororesin (PCM-I-19) because the visible light reflectivityis improved.

The present invention has made it possible to provide the technology forimproving brightness of light of an illuminator or a lightsignal-emitting instrument. The present invention has made possible notonly the improvement of the performance of these apparatus, but alsosecuring performance equivalent to the former with smaller energyconsumption than the former, and has also made possible the providing ofenergy saved apparatus. Therefore, it can be said that the presentinvention has a valuable industrial applicability.

1. A precoated metal sheet for light reflectors, comprising a metalsheet or plated metal sheet, a visible light reflective coat provided onone surface of the metal sheet or plated metal sheet, and a heatabsorptive coat provided on the other surface of the metal sheet orplated metal sheet, wherein the visible light reflective coat has adiffuse reflectance of visible rays of not less than 0.7 in a wavelengthof 400 to 700 nanometers, and the heat absorptive coat has a totalemissivity of infrared rays of not less than 0.7 in the range of wavenumber of 600 to 3000 cm⁻¹ measured at a certain temperature within therange of from 80 to 200 degrees centigrade.
 2. A precoated metal sheetfor light reflectors according to claim 1, wherein the visible lightreflective coat comprises a binder and a titanium oxide, a content ofthe titanium oxide being 40 to 250 parts by weight, based on 100 partsby weight of a solid content of the binder.
 3. A precoated metal sheetfor light reflectors according to claim 1, wherein the binder in thevisible light reflective coat comprises a fluororesin.
 4. A precoatedmetal sheet for light reflectors according to claim 1, wherein the heatabsorptive coat comprises a binder and a heat absorptive pigment, acontent of the heat absorptive pigment being 10 to 150 parts by weight,based on 100 parts by weight of a solid content of the binder.
 5. Aprecoated metal sheet for light reflectors according to claim 4, whereinthe heat absorptive pigment is a carbon.
 6. A precoated metal sheet forlight reflectors according to claim 4, wherein the heat absorptive coatfurther comprises a conductive metal powder, a content of the conductivemetal powder being from 1 to 50 parts by weight, based on 100 parts byweight of a solid content of the binder.
 7. A precoated metal sheet forlight reflectors according to claim 1, wherein the surface roughness Raof the metal sheet or plated metal sheet is 0.05 to 1.8 micrometers. 8.A precoated metal sheet for light reflectors according to claim 1,wherein the metal sheet or plated metal sheet is preferably a steelsheet or a plated steel sheet.
 9. An electric or electronic apparatuscomprising a precoated metal sheet for light reflectors according toclaim 1.